1. Field of Invention
The present invention relates to a filter, in particular for the separation of leucocytes from further blood components, having an outer sheath, having at least one intermediate layer which is a component of a frame or forms a frame, having an inlet chamber which is in communication with an inlet for the medium to be filtered and an outlet chamber which is in communication with an outlet for the filtrate, and having a filter material which separates the inlet chamber from the outlet chamber.
Filters of this kind are, for example, used to liberate blood or blood components from leucocytes prior to storage or to transfusion to the recipient, since said leucocytes can cause unwanted side effects. There is therefore a necessity to separate leucocytes and, optionally, further interfering materials prior to the storage or transfusion of the blood or of its components (e.g. erythrocites, plasma).
2. Description of the Prior Art
Filters of this kind are known in numerous different embodiments. The filter disclosed in EP 0 526 678 B2 has an outer sheath made of flexible material which is connected to an intermediate layer of two soft foils which form a frame. The filter material which separates the outlet chamber of the filter from the inlet chamber is received in the frame. The filter material is welded into the frame formed by the foils and has the effect in this manner that the blood to be filtered or the blood components to be filtered only have to flow through the filter surface to enter into the outlet chamber.
An embodiment of a filter is known from WO 01/91880 A1, wherein the outer sheath consists of two foils which are directly welded to one another. No intermediate layer is provided. The filter has in inwardly disposed welding seam and an outwardly disposed welding seam, with the outwardly disposed welding seam directly connecting the foils forming the outer sheath to one another and the inwardly disposed welding seam connecting the filter material to the outer sheath. A non-welded region comprising a filter medium is located between the two welding seams and is resilient due to the lack of a welding seam and damage during centrifuging can be largely avoided by means of it. The filter known from WO 01/91880 A1 has the disadvantage that it has stubs on both oppositely disposed sides of the outer sheath for the inlet of the blood and for the outlet of the filtrate respectively, whereby a flat surface is prevented on both sides of the filter which would be desired for the purpose of centrifuging.
There is a disadvantage with the filter apparatus known from EP 0 526 678 B2 in that dead spaces in which no blood can be filtered arise in the region of the frame encompassing the filter material. This is unwanted because, on the one hand, the available filter volume is not fully used. On the other hand, there is a disadvantage in that valuable blood components can accumulate in the dead spaces which cannot be regained or can only be regained with difficulty after the end of the filtration. The accompanying loss of blood components not regained is unwanted.